(1) Field of the Invention
The present invention relates to a communication method in a mobile communication system and a mobile station and a base station in the same system. The invention relates particularly to a technique suitable to improve the throughput of uplink data communication from the mobile station to the base station.
(2) Description of Related Art
In the current 3GPP (3rd Generation Partnership Project), standardization of W-CDMA. (Wideband-Code Division Multiple Access), which is one of the schemes of the third-generation mobile communication system, is in progress. One of the themes of the standardization is
the HSDPA (High Speed Downlink Packet Access) scheme which provides a great-capacity high-speed packet data transfer (about 14 Mbps at maximum) in the downlink direction from a base station to a mobile station. Further, the HSUPA (High Speed Uplink Packet Access) scheme, which can be regarded as HSDPA in the uplink direction from a mobile station to a base station, is under investigation (see, for example, the following non-patent document 1).
In such high-speed data transmission, data transmission scheduling for efficient sending-out of data packet is important. In HSUPA, scheduling is determined based on such information as reception quality, the amount of buffer remaining, priority, and so on. These information items are notified from a mobile station to a base station as Scheduling Information (SI) in form of an uplink transmission request prior to uplink transmission.
[Non-patent Document 1] 3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; “TS 25.309 V6.2.0 (2005-03) FDD Enhanced Uplink Overall Description Stage 2 (Release 6)”
In the present 3GPP specification, communication execution by HSUPA is performed after establishment of dedicated radio channels, and as procedures from call generation to call setting and HSUPA application, known procedures applied. Accordingly, delay occurs between a data transmission request on a terminal and actual data transmission.
For example, as shown in FIG. 25, a mobile station (UE: User Equipment) 100 sends an access request to a base station (BTS: Base Transceiver Station) 200 (step S100) by a random access method. Upon receipt of a reply to the access request from the base station 200 (step S200), the mobile station 100 sends a dedicated radio channel establishment request to the base station 200 (step S300). When a reply to the channel establishment request is received by the mobile station 100 (step 400), the mobile station 100 sends a transmission rate request to the base station 200 (step S500). When a rate is assigned by the base station 200 (step S600) in response to the transmission rate request, the mobile station 100 eventually starts data transmission (steps S700 and S900). Here, when the data transmitted is normally received by the base station 200, ACK is sent back to the mobile station 100, and when the data transmitted is not received normally, NACK is sent back to the mobile station 100 (step S800). Upon receipt of NACK, the mobile station 100 performs data retransmission.
Under a condition where the data rate is low, delay caused by such negotiation prior to actual uplink data transmission is inconspicuous, but as the data rate increases, the delay becomes a considerable problem. In addition, for realization of “Always on” by radio, it is preferable that connection delay be as small as possible.